Evaluation of the effects of anti-pruritic drugs on scratch responses using histamine H₁ receptor-deficient mice

The effects of anti-pruritic drugs on scratching behavior associated with passive cutaneous anaphylaxis in histamine H₁ receptor-deficient and wild-type mice were studied. Passive sensitization with mouse monoclonal anti-dinitrophenyl-immunoglobulin E (IgE) resulted in an increase in the incidence of scratching behavior induced by intravenous injection of dinitrophenyl-ovalbumin in both wild-type and histamine H₁ receptor-deficient mice. The histamine H₁ receptor antagonist diphenhydramine inhibited scratching behavior induced by antigen in passively sensitized wild-type mice, whereas no effect was observed in histamine H₁ receptor-deficient mice. On the other hand, oxatomide inhibited scratching behavior in both mice, although the effect in wild-type mice was more potent than that in histamine H₁ receptor-deficient mice. Tranilast inhibited scratching behavior with the same potency in both mice. We concluded that the scratching behavior associated with passive cutaneous anaphylaxis involves not only histamine H₁ receptors but also other chemical mediators. Furthermore, the results of the present study indicated that oxatomide has an antagonistic effect on histamine H₁ receptors as well as anti-pruritic effect in vivo.